I don't know...it's more believable to me than a lot of other theories. Serial Killers and the like are crazy anyway. They do leave "calling cards" sometimes too, that's not very uncommon.
Look at Luke Helder who tried to pipe bomb people in the upper midwest in 2002 and if you drew it on a map, it was a smiley face. That's pretty unbelievable too but it was still true.
Also, SFK was formulated by two retired NYC detectives who have more experience in the field than all of us combined and probably know what they're talking about any second of the day more than us.
Anyway, it's much more plausible in my mind than bigfoot.